Printing by electrical attraction of inks

ABSTRACT

PRINTING IS EFFECTED BY FIRST PLACING AN ELECTRIC CHARGE OVER THE COATED SURFACE OF A ZINC OXIDE COATED WEB OF PAPER. THIS CHARGE IS NEUTRALIZED IN SELECTED IMAGE AREAS BY A PROJECTED LIGHT IMAGE. THE WEB IS THEN PASSED BETWEEN A GROUND ELECTRODE AND A SMOOTH INK BEARING CONDUCTIVE DRUM CHARGED TO A POTENTIAL ON THE ORDER OF THAT OF THE UNNEUTRALIZED PORTIONS. LIQUID INK FROM THE DRUM IS BODILY ATTRACTED FROM THE DRUM TO THE NEUTRALIZED IMAGE AREAS IN AN UNSUPPORTED COLUMN.

Feb. 2, 1971 E. P. DAMM, JR I 3,560,204

PRINTING BY ELECTRICAL ATTRACTION OF INKS Filed Ngv. 7. 1966 INVENTOREUGENE R DAMM JR.

BY U,

AT TORNE Y United States Patent Oflice Patented Feb. 2, 1971 3,560,204PRINTING BY ELECTRICAL ATTRACTION OF INKS Eugene P. Damm, Jr.,Poughkeepsie, N.Y., assignor to International Business MachinesCorporation, Armonk N.Y., a corporation of New York Filed Nov. 7, 1966,Ser. No. 592,547 Int. Cl. G03g 13/10, 13/22 US. Cl. 96-1 11 ClaimsABSTRACT OF THE DISCLOSURE Printing is effected by first placing anelectric charge over the coated surface of a zinc oxide coated web ofpaper. This charge is neutralized in selected image areas by a projectedlight image. The web is then passed between a ground electrode and asmooth ink bearing conductive drum charged to a potential on the orderof that of the 'unneutralized portions. Liquid ink from the drum isbodily attracted from the drum to the neutralized image areas in anunsupported column.

Generally stated, it is an object of this invention to provide for animproved method of attraction for liquid ink printing.

More specifically it is an object of this invention to provide for usingelectrical attraction for attracting a liquid ink to the surface of acoated web.

Another object of the invention is to provide for placing anelectrostatic charge on the coated surface of a web, neutralizing thecharge in an image area, and then utilizing a relatively high voltage toprovide a potential difference between the image area and an ink-bearingdrum sufiicient for attracting a liquid ink bodily to the neutralizedarea.

Yet another object of this invention is to provide for using a watersoluble acid or basic dyestuff as a self-fixing ink in an electricalprinting process.

Still another object of the invention is to provide for using aphoto-sensitive material coated paper as a base in a printing processand for electrically attracting a liquid ink to the coated surface ofthe paper in predetermined pattern areas.

It is also an object of the invention to provide for placing an electriccharge on the zinc oxide coated surface of a Web, removing the chargefrom an image area of the coating and using an electrical potential forattracting a liquid water soluble dyestuff ink to the image area.

Another important object of the invention is to provide for placingnegative electric charge on the zinc oxide coated surface of a paperweb, neutralizing the charge in discrete image areas by exposing suchareas to selected light images, and attracting a self-fixing Watersoluble acid or basic dyestuff ink to the neutralized areas from anegatively charged ink drum.

Yet another important object of this invention is to provide in printingprocesses for establishing an image area on the surface of a coated webhaving a different surface charge than the surrounding area, and usingan ink drum connected to a source of potential of a value sufficient toestablish a field for raising an unsupported column of liquid ink to thesurface of the Web in the shape of the image.

Another important object of the invention is to provide for using in aprinting process water soluble ink solutions which are attracted to thecoated surface of a web by an electrical image field.

In accordance with a preferred embodiment of the invention,electrostatic charge is placed on the coated surface of a zinc oxidecoated web of paper. The charge is neutralized in selected image areasby projecting an image thereon by means of a beam of light passingthrough an image-bearing mask. The Web is thereupon passed between aground electrode and an ink-bearing drum charged to a potential on theorder of the remaining surface charge. The liquid ink is attractedbodily across the gap between the drum and Web in the image neutralizedareas to provide well-defined character images with extremely lowbackground effect.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawing.

In the drawing:

The single figure is a schematic diagram of apparatus for printing on acoated web according to a preferred embodiment of the invention.

Referring to the drawing, the reference numeral 10 denotes generally aweb of coated paper having for example a zinc oxide coating 10a on oneside. The web 10 is passed between a 3-wire corona unit 12 positioned onthe coated front side of the web in conjunction with a ground plate 14on the back side of the web for placing an electrical charge on thecoated surface 10a. The web 10 is then passed through the projectionarea 15 of a projection system 16 comprising a lamp 17, an image-bearingmask 18 and a lens 20 for projecting onto the coated and changed surfaceof the web the image or images of characters which are to be printed onthe web. This neutralizes the charge on the coated surface in the imagearea. The web 10 is then passed around a roller 22 and through an airgap 24 between a ground electrode 26 and ink-bearing drum 28 which dipsinto an ink supply 30 contained in a tray 32. A doctor blade 33 isspaced from the drum to establish the desired ink film thickness as thedrum rotates. The drum 28 is conductive and is connected to a source ofpotential at terminal 34 so as to provide an electric field in the airgap 24 corresponding to the character image of the particularneutralized area on the web 10. This field provides for raising the inkbodily from the surface of the drum 28 in an unsupported column havingthe shape of the neutralized image area to form ink images on the coatedsurface of the web 10 corresponding to the neutralized image areas. Inkrupture results from the tensile forces set up as the ink drum and paperdiverge.

In practice, a web of zinc oxide coated electrophotographic paper 10(Bruning No. 32-15 55Premium Copy) has been used with a standard 3-wirecorona unit having three 3-mil wires spaced approximately one-fourth ofan inch from the web and charged to a potential on the order of -5,000volts. The lamp 17 comprised a type 1531A General Radio StroboscopicFlash Unit. The ground electrode 26 had a 60 degree included angle witha 10-n1il fiat surface at the apex, and with an ink film on the order of.0015 inch thick the air gap 24 was on the order of .0032 inch. With 600volts applied to the ink drum 28 of stainless steel, paper speed was sixinches per second. The air gap through which the liquid ink jumps may beas high as .0032 inch. By varying experimental conditions printingspeeds up to 60 inches per second were obtainable.

Using a zinc oxide coated paper, either acid or basic dyestuffs providesan excellent ink in a water solution. Examples are:

1 Similar to C. I. Acid Blue 127.

A 1% solution of any of the above in water provides, because of theamphoteric nature of the zinc oxide, a self-fixing action without theuse of resin binders.

Most of the copying has been accomplished with a zinc oxide coated paperusing negatives as the projection medium. However, positives can be usedfor copying, merely by electrically grounding the ink drum or by puttinga potential on the drum opposite to that on the paper.

In line with the use of coated papers, an electrostatic charge image canbe written on dielectric materials or paper coated with a dielectricmaterial, thus rendering the process useful for straight outputprinting. Images in general would no longer be produced by way of aprojected image but would be produced by means of conductive rubberrollers containing raised characters for printing standard forms, ormatrix type of write-heads applying electric pulses for printingvariable information.

By using a non-absorbent photo-conductor such as selenium, or a zinccadmium sulfide coating, the deposited ink could then be transferredfrom the web to ordinary paper. This essentially is an off-set techniquewhich permits the use of ordinary paper and the re-use of the conductorweb.

Instead of using an acid or basic dyestutf and a water solution as theink, carbon black ink has been used which is essentially a colloidalsuspension of 35% by weight of carbon black of a particle size '28 mu inwater of which 61 grams were diluted to 1000 millimeters withdemineralized water. While this ink is satisfactory on ordinary paper,on coated paper it tends to smear when used by itself since there islittle or no soaking of the ink into the paper. The addition of a resinbinder such as polyvinyl alcohol can be added; to remedy this situation.Approximately .25 of Du Pont Evanol 51-05 would be satisfactory.Nonpolar liquids such as toluene or nitrile silicone could be used, butthey do not jump the gap as rapidly as the water based solutions. Alsotheir response times are affected somewhat by relative humidity unlesspolarizing particles such as colloids are used.

From the above description and the accompanying drawing, it will be seenthat water soluble inks utilizing acid or basic dyestuifs may be readilyattracted electrically to a selectivity charged coated web for providingclearly defined printed character images. The use of a resin binder isavoided when zinc oxide coated paper is used with these dyes as theytenaciously cling to the paper due presumably to the amphoteric natureof the zinc oxide, and produce image fixation without the use of resinbinders.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. A method of printing comprising the steps of,

producing an electric charge on predetermined areas of the coatedsurface of a web prior to development, and

then attracting ink as an unsupported column to uncharged portions ofthe coated surface by transversing the web between aground electrode andin spaced relation relative to a smooth ink-coated conductive drumrotating in the same direction as the web so as to provide apredetermined gap between the drum and the coated surface, said drumbeing connected to a potential source having a potential such as toprovide a potential difference between the drum and said unchargedportions of the coated surface to attract ink from the drum theretoacross said gap.

2. A method of printing as defined in claim 1 characterized by the webcomprising a photo-sensitive coated paper.

3. A method of printing as defined in claim 2 characterized by thephotosensitive coating comprising a zinc oxide coating.

4. A method of printing as defined in claim 1 characterized by initiallyplacing a substantially uniform charge on the coated surface and thecharge in the image area being neutralized by projecting a light imageon selected portions of the charged surface.

5. A method of printing as defined in claim 1 characterized by thecoated surface of the paper and the inkcoated drum having an air gap onthe order of .0030

inch across which the ink is bodily attracted.

6. A method of printing as defined in claim 1 characterized by the inkbeing a water-based solution.

7. A method of printing as defined in claim 1 characterized by the inkcomprising a colloidal suspension of carbon black in water.

8. A method of printing as defined in claim 1 characterized by the inkcomprising a solution in water of a dyestuif.

9. A method of printing as defined in claim 1 characterized by the inkcomprising a Water-based acid or basic dyestutr'.

10. A method of printing as defined in claim 1 characterized by theattraction of an unsupported column of a water-based ink to a latentimage area on a hydro- 40 phobic substrate.

11. A method of printing as defined in claim 1 characterized by thecoated surface of the web being amphoteric in nature so that either acidor basic dye inks can be used and the reaction therebetween obviates thenecessity for a resin binder.

References Cited UNITED STATES PATENTS 3,084,043 4/1963 Gundlach 96-13,232,190 2/1966 Willmott 96--1X 3,256,855 6/1966 Oliphant 117-37LX3,383,209 5/1968 Cassiers et al. 96l.3 3,435,802 4/ 1969 Nail 117--93.4X

GEORGE F. LEsMEs, Primary Examiner C. E. VAN HORN, Assistant ExaminerUS. Cl. X.R. 117-37; 252-62.1

